The invention relates to a process and an apparatus for the heating of pasty materials by surface and infusion type heating.
The heating of pasty materials to high temperature is a frequent task in the industry (e.g. for the purpose of sterilization) by surface heat exchangers or apparatus used for direct heating.
A considerable part of the materials to be processed in the chemical-, pharmaceutical- and food-industry is heat-sensitive. Depending on the processed material, increase of the temperature is detrimental to the components of the material. The major part of the presently used apparatuses are heat exchangers, the various constructions of which may be suitable for the fast heating of the pumped products.
If the viscosity of the product to be processed is high, then from the viewpoint of the effective heat transfer and hydraulic resistance of the apparatus, only those of special construction may come into consideration. The highly viscous pasty materials in most cases contain solid components as well. The optimal processing of this kind of materials is not possible with the presently existing technical solutions.
The realization of the direct heating appears to be feasible for the fast heating of pasty materials. Such apparatuses are used for the heat treatment of liquescent materials in apparatuses functioning with injection or infusion system. The heating of pasty materials in such apparatuses raises serious technical problems.
In case of using infusion type apparatuses, the perfect mixing of the heating medium and the material is difficult to solve, due to the high viscosity.
When infusion type heaters are used where the product is atomized in the steam chamber, the high viscosity and the pressure of incidental solid components represent similar problems.
In case of using nozzles under pressure with one or two mediums, high differential pressure is required to bring about the atomization and the exit velocity of the liquid jet is also high. When drop aggregation with small characteristic size which is appropriate to the process is brought about, the differential pressure in the nozzle and the exit velocity exclude the use of infusion system, since it results in rather large dimensions of the apparatus.
Apart from the characteristic drop size obtained by atomization, the exit velocity influences the size of the heating chamber to a considerable extent. The direct heating takes place in the heating chamber where the heating medium is in direct contact with the drop emerging from the nozzle. The time of heat conduction required for the temperature determining the heat treatment is influenced, apart from the drop size, by the characteristics of the material. In order to provide adequate time for the heat conduction the drops should be in contact with the heating medium without agglutination of the drops. This reaction time determines the size of the heating chamber. In case of high exit velocity this may considerably increase the dimensions of the apparatus.
The diameter of the heating chamber is influenced by the size of the cone of dispersion emerging from the nozzle. In case of large cone of dispersion the diameter increses considerably which leads to the excessive increase of the wall thickness of the apparatus.
The use of disc atomizer in infusion type apparatus is not suitable either, since it similarly increases the diameter of the apparatus.